Control apparatus



g- 4, 1942- D. E. RICHARDSON 2,292,159

CONTROL APPARATUS Filed June 28, 1941 Jhflnfarx fiona/al Efiz'c/Eardsozz 15y 2% W4 urn (1 5 Patented Aug. 4, 1942 UNETED STATESPATENT GEHCE 8' Claims.

This invention relates to electronic control apparatus and particularlyto safety control apparatus of the character in which electron tubes areadapted to be maintained in a nonconductive state during normaloperation of the equipment with which the control apparatus isassociated, and Where these tubes are arranged to become conductive onlyin the event an unsafe condition arises with respect to the equipment orin the control apparatus itself.

In apparatus of the character to which the present invention pertains itis, of course, essential that when a tube is called upon to pass currentthrough its plate or anode circuit that it should be capable of sodoing; which is to say, that the conductivity of the tubes should notbecome so impaired that any tube remains in a permanently nonconductivstate. In order to insure that the tubes are at all times capable offunctioning as desired it is customary to regularly check the tubes andreplace any which have become defective. However, where this is donemanually there is always the likelihood that a proper check will not bemade and that defective tubes will be allowed to remain in use, therebygiving rise to a hazardous situation because of the possible failure ofthe control apparatus to react safely in an emergency. Hence, an objectof th present invention is to enable the control apparatus toautomatically detect failure of one or more electron tubes and to causeit to function in a saf manner if and when such a condition arises, andinasmuch as one of the chief causes of tube failure is burning out ofthe filament or heater of the tube, the present invention isparticularly designed to detect the occurrence of an unsafe condition ofthis character.

In the copending application of Robert E. Yates, Serial No. 245,17 3,filed December 12, 1938, it has been proposed to automatically detectfailure of a filament in any of a plurality of electron tubes byconnecting all of the filaments in a series circuit which includes adevice responsive to an interruption in the flow of current through theseries circuit to cause the apparatus to react as though to an unsafecondition. While this scheme is applicable where vacuum tubes are beingemployed, it is not equally feasible where the electron tubes are of thegas-filled type because if the filaments of these tubes are connected inseries with each other electrical stresses are apt to be set up betweenthe cathodes and filaments and this may in some instances causedisruptive discharges to take place within the tubes. Hence,

where gas-filled tubes are used it is advisable to connect the filamentsthereof in parallel to the voltage supply source, with the cathodes ofthe tubes so arranged as to be electrically at the midpoints of theirrespectiv filaments, or else to provide a separate voltage supply sourcefor each filament.

In the copending application of Donald E. Richardson and Robert E.Yates, Serial No. 400,332, filed June 28, 1941, there is disclosed acontrol apparatus utilizing gas-filled tubes which are arranged to bemaintained in a non-conductive state so long as a fuel burner or likesystem with which the control apparatus is associated is in normaloperation, such tubes becoming conductive only in the event of anemergency requiring functioning of th control apparatus. This particularapparatus includes means for automatically checking the conductivity ofeach tube as a condition precedent to operation of the system, and ifeach tube is capable of conducting current the system is thenconditioned for operation. It may be desirable to augment this initialconductivity test by making provision for a continuous check on thecondition of the tube filaments all the time the control apparatus isbeing utilized, and hence it is another object of the present inventionto afford such a check while the system is in operation without the ncessity of connecting the filaments of the various tubes in series.

A more specific object is to match the impedances of two or more equallydivided groups of filaments and to control the operation of theapparatus in dependence upon whether or not the impedances are evenlybalanced electrically. An ancillary object is to provide a novelbalancer system of transformers having a neutral connection throughwhich the flow of current is regulated according to the relative loadson two or more of the transformers, where each transformer loadcomprises the combined impedance of a group of tube filaments, and tocause the ,control apparatus to function as though in response to anunsafe condition whenever a substantial current flow is set up in theneutral connection as a result of an unbalancing of load impedancesindicative of a filament failure.

While the present invention is described herein as being particularlyadapted for use in conjunction with a control apparatus for a fuelburner or like system, it will be understood that it is capable of moreextensive applications wherever electronic control apparatus isemployed, and hence it is to be understood that the invention is notlimited to th exact use herein disclosed.

Other and further objects of the present invention will be apparent fromthe following description and claims and will be understood by referenceto the accompanying drawing which, by way of illustration, shows apreferred embodiment and the principle thereof and what I now considerto be the best mode in which I have contemplated applying thatprinciple. Other embodiments of the invention embodying the same orequivalent principle may be used and structural changes may be made asdesired by those skilled in the art without departing from the presentinvention and the purview of the appended claims.

The accompanying drawing is a diagrammatic illustration of my invention.

Referring to the drawing, the various elec tron tubes included in anelectronic control apparatus are in the present instance shown dividedinto two groups, the tubes in one group being designated by thereference character I and those in the other group by the referencecharacter I. The filaments 2 of the tubes I are connected in parallel bya pair of conductors 3 and 4 to the secondary 5 of a filament voltagesupply transformer 6. Likewise, the filaments 2 of the tubes I areconnected in parallel across the conductors 3' and 4 which lead to thesec ondary 5' of a filament voltage supply transformer 6. An equalnumber of tube filaments are arranged to be supplied with voltage by thetransformers 6 and 6', and if it should happen that there is an oddnumber of tubes in the apparatus, a balancing resistance is connected inparallel with the filaments in the group having the lesser number, theobject being to equalize the loads on the transformers 6 and 6. Thecathodes I of the tubes l are preferably connected by a common conductor8 to a center tap on the secondary 5 so that these cathodes will beelectrically at the midpoints of the filaments 2.

Similarly, the cathodes I of the tubes I' are connected by a commonconductor 8 to a center tap on the secondary 5'.

One end of the primary winding 9 of the transformer 6 is joined atjunction Ill to one end of the primary winding 9 of the transformer 6,while the opposite ends of the primaries 9 and 9' are connected byconductors II and II, respectively, to the ends of a secondary I2 of atransformer I3. The primary I4 of this transformer I3 is adapted to beenergized from a suitable source of alternating current for operatingthe apparatus. The secondary I2 has a center tap I5 from which aconductor I6 leads to a junction or terminal I! of a resistor I8, theother terminal I9 of the resistor I8 being connected by a conductor 20to the junction II] of the primaries 9 and 9'. The conductor 20 and theresistor I8 together constitute a neutral path or connection generallydesignated 2| extending between the junctions I1 and I0. Normally whenthe loads on the filament transformers 6 and (5' are sub stantiallyequally balanced, the secondary I2 of the transformer I3 suppliesalternating current solely through the conductors II and II to theseries-connected primary windings 9 and 9 of the transformers 6 and 6',and substantially no current flows through the path 2I. However, if afilament in one of the tubes burns out, for example, a filament 2 in atube I, the load impedance on the secondary side of the correspondingfilament transformer as 6 becomes greater than the impedance on thesecondary side of the other transformer as 6', producing an unbalancedload condition, and under these circumstances current flows through thepath 2I. The phase relation of this current with respect to theimpressed voltage depends upon which of the transformers 6 and 6' hasthe heavier load, as will be explained in greater detail presently.

In order to detect an unbalanced load condition, a pair of electrontubes 22 and 22 are arranged with their cathodes 23 and 23' connected incommon to the terminal I! of the resistor I8, while the anodes 24 and 24of these tubes are respectively connected through the windings of relays25 and 25 to the conductors II and II. In this manner the tubes 22 and22 are adapted to be alternately rendered conductive to pass currentthrough the windings of the relays 25 and 25 during alternatehalf-cycles of the impressed voltage. The relays 25 and 25 are of thealternating-current type and are provided with contacts 26 and 26 whichare normally open when the relays are deenergized but which aremaintained closed so long as the relays are energized by the currents inthe anode circuits of the tubes 22 and 22.

The control apparatus to which my invention pertains is particularlyadapted to be used in combination with a fuel burner system as disclosedin the aforesaid copending application, Serial No. 400,332. Such asystem includes a fuel valve 27 which is operated by a solenoid 28 forenabling fuel to be supplied to the burners in the system. Whenever anabnormal condition such as failure of combustion arises, however, thesolenoid 28 is adapted to be deenergized by the control apparatus toenable the fuel valve 21 to close. For the purpose of enabling theoperation of the solenoid 28 to be controlled in part according to thecondition of the tube filamerits, the relay contacts 26 and 26 areembodied in the circuit 29 through which the solenoid 28 is energized,this circuit extending through the contacts 26 and 26 in series whenboth of these contacts are closed. Since the relays 25 and 25 are bothmaintained energized under normal load conditions, the contacts 26 and26 thereof remain closed so that there is no interruption of the circuit29 insofar as these contacts are concerned.

The tubes 22 and 22', which are preferably of the gas-filled type, havecontrol grids 30 and 30 which are connected through protective resistors3| and 3| to the terminal I9 of the resistor I8. It will be recalledthat the cathodes 23 and 23 are connected to the opposite terminal I! ofthis resistor. Hence, if any current flows through the resistor I8 thecontrol grids 30 and 3| may become biased with respect to their cathodes23 and 23' due to the voltage drop in the resistor I8. The filaments 32and 32' of the tubes 22 and 22 have been fragmentarily represented inthe drawing but it is to be understood that these filaments will besupplied by voltage from a suitable source which may be independent ofthe transformers 6 and 5. In this connection it should be noted thatinasmuch as the tubes 22 and 22' are adapted to be normally maintainedin a conductive condition when the filament loads are evenly balanced(each tube being rendered nonconductive only when there is a filamentfailure in the corresponding group of filaments 2 or 2' as will beexplained presently) it is not essential that the conductivity of thetubes 22 and 22' should be continually checked in the manner in whichthis is done in the case of the tubes I and I, because if a tube 22 or22' becomes perin'anentl'y ncnconductive it immediatelycauses theholding circuit for the solenoid 28 to be broken so that the apparatusfails safely. However, to avoid providing extra filament transformersfor the tubes 22 and 22 it may be desirable to connect the filaments 32and 32' in parallel with the filaments 2 and 2, respectively, in orderthat they may be supplied with current by the transformers 6 and 6. Inthis event the filaments 32 and 32' are included in the load impedanceswhich are to be matched against each other, but of course this is onlyincidental to the purpose of minimizing the number of transformers whichare required.

As an example of the manner in which the apparatus operates, it will beassumed that one of the filaments 2 of the tubes l' burns out, therebyrendering its tube ermanently nonconductive. As a result of this thetotal load impedance on the secondary 5 of the filament transformer 6increases in value, producing an unbalanced load condition. During thosehalf-cycles of the alternating current in which the conductor II ispositive with respect to the conductor I I, current flows through thepath 2| in a direction away from the junction I1 toward the junction It.By reason of the voltage drop in the resistor It! the terminal I9becomes negative with respect to the terminal I! during thesehalf-cycles of the alternating current, thereby causing a negative biasto be applied on the control grid of the tube 22. This is effective toprevent the tube 22 from conducting current, so that the relay 2Sthereupon deenergizes and opens its contact 25. The circuit 23 for thesolenoid 28 is thus broken, causing the solenoid 28 to deenergize andthe fuel valve 2! to close and thereby interrupt the operation of theburners in the system. The tube 22' is unaffected under the conditionsjust assumed because during the halfcycles in which the conductor I I ispositive with respect to the conductor II, current flows through thepath 2! in a direction toward the junction or terminal II. This producesa voltage drop in the resistor I 8 of such polarity as to impart apositive bias to the control grid 30 so that the tube 22 is notprevented from conducting current.

If a filament 2 of one of the tubes I should burn out to thereby producean unbalanced load condition, current flows through the path 2| in adirection away from the junction I1 during those half-cycles of thealternating current in which the conductor II is positive with respectto the conductor II, that is to say, during those half-cycles duringwhich the tube 22 is normally rendered conductive. Because of thevoltage drop produced in the resistor I8 by the current flowing throughthe path 2|, the junction I9 becomes negative with respect to thejunction I1 and thereby a negative bias is impressed upon the controlgrid 39' of the tube 22. The tube 22 is thus rendered continuouslynonconductive and the relay 2'5 thereupon deenergizes to open itscontact 26 and thus break the circuit 29, with the aforesaid effects.The tube 22 continues to conduct current during those half-cycles whenthe conductor II is positive with respect to the conductor II becausethe phase of the current flowing through the path 2| is such that thecontrol grid 30 receives a positive bias due to the voltage drop in theresistor I8.

It will thus be seen from the foregoing that whenever a filament in anyof the tubes I or I becomes defective so that its conductivity isimpaired, either one or the other of the tubes 22 or 22 will cease toconduct current and thereby deenergize its relay 25 or 25 to break thecircuit 29. The control apparatus may be so arranged that even amomentary interruption of the circuit 29 is sufficient to permanentlydisable this circuit even though a balanced load condition is restored,this being common practice in the art and hence not disclosed in detailherein. This is of utility in the event, for example, that one of thefilaments 2 burns out, producing an unbalanced load condition, andshortly thereafter a filament 2 burns out to again equalize the loads.The possibility that there will be a simultaneous failure of an equalnumber of filaments 2 and 2 while the apparatus is in operation is soremote that for practical purposes it need not be considered. The tubes22 and 22 react safely in the event a filament 32 or 32 burns out,inasmuch as this causes the tube to cease conducting and deenergize itsrelay 25 or 25' to thereby open the circuit 29.

Where the number of tubes I and I" in the apparatus becomes quite large,it may be advisable to have more than two groups of tubes, in whichevent the various groups can be paired together and the filament loadsbalanced against each other in a manner similar to that explainedhereinabove.

Another advantage of the illustrated apparatus is that it enables theoperator to readily ascertain in which group the defective filament maybe found. Thus, if there is a burned-out filament in one of the tubesdesignated I, the tube 22 lights; whereas if the filament burn-out hadoccurred in one of the tubes designated I, then the tube 22 would light.It will be understood, of course, that it is not essential to useelectron tubes as 22 and 22 for detecting current flow in the neutralconnection 2|, any current-responsive means being suitable for thispurpose.

Thus, while I have illustrated and described a selected embodiment of myinvention, it is to be understood that it is capable of variation andmodification and I therefore do not Wish to be limited to the precisedetails set forth but desire to avail myself of such changes andalterations as fall within the purview of the following claims.

I claim:

1. In an electronic apparatus adapted to be operated from a source ofelectric current for controlling the operation of associated equipmentand including a plurality of electron tubes adapted to be nonconductivewhen said equipment is operating normally and to become individuallconductive in response to abnormal conditions arising with respect tocorresponding parts of said equipment, each of said tubes including afilament adapted when energized to condition its tube for the conductionof current, the combination therewith of means electricallyconnectingthe filaments of a group of said tubes in parallel to therebyafford a first load impedance, means electrically connecting thefilaments of a group of tubes equal in number to the firstnamed group inparallel to afford a second load impedance, means individually couplingsaid load impedances in a circuit with said source of current forthereby energizing all of said filaments, said circuit extending throughthe coupled load impedances in series, means provid ing a neutralconnection between said source of current and a point in said seriescircuit electrically intermediate the coupled impedances;

said load impedances, said circuit and said neutral connection being soconstituted and arranged as to afford a normally balanced network inwhich said neutral connection normally conducts substantially nocurrent, said network becoming unbalanced to enable said neutralconnection to conduct current only when said impedances are of unequalvalue due to failure of a filament in any of said groups of tubes; andmeans responding to a fiow of current in said neutral connection forindicating the fact that a tube has been rendered permanentlynonconductive by reason of the aforesaid filament failure.

2. In an electronic apparatus adapted to be operated from a source ofelectric current for controlling the operation of associated equipmentand including a pair of electron tubes adapted to be nonconductive whensaid equipment is operating normally and to become individuallyconductive in response to abnormal conditions arising with respect tocorresponding parts of said equipment, each of said tubes including afilament having a predetermined impedance and adapted when energized tocondition its tube for the conduction of current, the combinationtherewith of means individually coupling said filament impedances in acircuit with said source of current for thereby energizing saidfilaments, said circuit extending through the coupled impedances of saidfilaments in series, means providing a neutral connection between saidsource of current and a point in said series circuit electricallyintermediate the coupled impedances; said impedances, said circuit andsaid neutral connection being so constituted and arranged as to afford anormally balanced network in which said neutral connection normallyconducts substantially no current, said network becoming unbalanced toenable said neutral connection to conduct current only when saidimpedances are of unequal value due to failure of a filament in eitherof said tubes; and means responding to a fiow of current in said neutralconnection for indicating the fact that a tube has been renderedpermanently nonconductive by failure of its filament,

3. In an electronic apparatus adapted to be op .erated from a source ofalternating current for controlling the operation of associatedequipment and including a pair of electron tubes adapted to benonconductive when said equipment is operating normally and to becomeindividually conductive in response to abnormal conditions arising withrespect to corresponding parts of said equipment, each of said tubesincluding a filament having a predetermined impedance and adapted whenenergized to condition its tube for the conduction of current, thecombination therewith of a pair of transformers each having primar andsecondary windings, means connecting the primary windings of saidtransformers in series with each other and in circuit with said sourceof current, means individually connecting the secondary windings of saidtransformers respectively to said filaments for thereby enabling saidfilaments to be energized by said source of current, means providing aneutral connection between said source of current, and the junction ofsaid primary windings; said transformers, said series circuit means andsaid neutral connection being so constituted and arranged as to afford anormally balanced network in which said neutral connection normallyconducts substantially no current, said network becoming unbalanced toenable said neutral connection to conduct current only when saidimpedances are of unequal value due to failure of a filament in eitherof said tubes; and means responding to a flow of current in said neutralconnection for indicating the fact that a tube has been renderedpermanently nonconductive by failure of its filament.

4. In an electronic apparatus adapted to be operated from a source ofalternating current for controlling the operation of associatedequipment and including a plurality of electron tubes adapted to benonconductive when said equipment is operating normally and to becomeindividually conductive in response to abnormal conditions arising withrespect to corresponding parts of said equipment, each of said tubesincluding a filament adapted when energized to condition its tube forthe conduction of current, the combination therewith of meanselectrically connecting the filaments of a group of said tubes inparallel to thereby afford a first load impedance, means electricallyconnecting the filaments of a group of tubes equal in number to thefirst-named group in parallel to afford a second load impedance, a

pair of transformers each having primary and secondary windings, meansconnecting the primary windings of said transformers in series with eachother and in circuit with said source of current, means individuallyconnecting the secondary windings of said transformers respectively tosaid load impedances for thereby enabling said filaments to be energizedby said source of current, means providing a neutral connection betweensaid source of current and the junction of said primary windings; saidtransformers, said series circuit means and said neutral connectionbeing so constituted and arranged as to afford a normally balancednetwork in which said neutral connection normally conducts substantiallyno current, said network becoming unbalanced to enable said neutralconnection to conduct current only when said impedances are of unequalvalue due to failure of a filament in any of said groups of tubes; andmeans responding to a flow of current in said neutral connection forindicating the fact that a tube has been rendered permanentlynonconductive by reason of the aforesaid filament failure.

:5. In an electronic apparatus adapted to be operated from a source ofalternating current for controlling the operation of associatedequipment and including a plurality of electron tubes adapted to benonconductive when said equipment is operating normally and to becomeindividually conductive in response to abnormal conditions arising withrespect to corresponding parts of said equipment, each of said tubesincluding a filament adapted when energized to condition its tube forthe conduction of current, the combination therewith of meanselectricall connecting the filaments of a group of said tubes inparallel to thereby afford a first load impedance, means electricallyconnecting the filaments of a group of tubes equal in number to thefirst-named group in parallel to aiford a second load impedance, a pairof transformers for individually coupling said load impedances in acircuit with said source of current to thereby energize all of saidfilaments, and means cooperating with said transformers and said sourceto afford a balancer network effective to compare the values of thecoupled load impedances, said network being arranged to remain in aneutral state so long as said load impedances have like values andresponding to an unbalanced load condition caused by filament failure ineither of said groups of tubes to give an indication of an unsafecondition of said apparatus.

6. In an electronic apparatus adapted to be operated from a source ofalternating current for controlling the operation of associatedequipment and including at least two electron tubes adapted to benonconductive when said equipment is operating normally and to becomeindividually conductive in response to abnormal conditions arisingwithrespect to corresponding parts of said equipment, each of said tubesincludin a filament having a predetermined impedance and adapted whenenergized to condition its tube for the conduction of current, thecombination therewith of a pair of transformers for individuallycoupling said filament impedances in a circuit with said source ofcurrent to thereby energize each of said filaments, and meanscooperating with said transformers and said source to aiford a balancernetwork effective to compare the values of the coupled impedances, saidnetwork being arranged to remain in a neutral state so long as said loadimpedances have like values and responding to an unbalanced loadcondition caused by filament failure in either of said tubes to give anindication of an unsafe condition of said apparatus.

7. In an electronic apparatus adapted to be operated from a source ofalternating current for controlling the operation of associatedequipment and including a plurality of electron tubes each including afilament effective when energized to condition its tube for theconduction of current, said tubes being adapted to be nonconductive whensaid equipment is operating normally and to become individuallyconductive in response to abnormal conditions arising with respect tocorresponding parts of said equipment, the combination therewith of afirst transformer having a primary winding connected to said source ofcurrent and including a secondary winding provided with a center tap andtwo end taps, second and third transformers having equal transformerratios and each including a primary winding and a secondary winding,means connecting the pri mary windings of said second and thirdtransformers in series with each other in a circuit extending betweenthe end taps of said first transformer, means separately connecting thesecondary windings of said second and third transformers to respectivelyassociated groups of said tube filaments for thereby enabling saidfilaments to be energized by said source of current, said groups offilaments being so arranged as to afford equal load impedances, meansproviding a neutral connection between the center tap of said firsttransformer and the junction of the primary windings of said second andthird transformers; said transformers, said connecting means and saidneutral connection being so constituted and arranged as to afford anormally balanced network in which said neutral connection normallyconducts substantially no current; and control means responsive to aflow of current in said neutral connection whenever said load impedancesbecome unbalanced due to the failure of a filament in either of saidgroups for effecting a control operation with respect to said equipment.

8. An apparatus as set forth in claim 7, in which said neutralconnection embodies a resistor and wherein said control means comprisesa pair of electron tubes arranged to be biased in dependence upon thevoltage drop set up in said resistor when current flows through saidneutral connection, such biasing voltage serving to render at least oneof said pair of tubes nonconductive, and means responsive to said pairof tubes and operating when either tube is rendered nonconductive tointerrupt operation of said equipment.

DQNALD E. RICHARDSON.

